The invention is related to a method and apparatus for determining the inflation status of a vehicle pneumatic tire as the tire rolls over the apparatus and while the tire is attached to the vehicle. Access to the tire valve stem is not required.
1. Field of the Invention
U.S. Pat. Nos. 5,445,020 and 5,396,817 issued to Rosensweig disclose tire inflation sensors for making a series of point measurements and determining the pressure of a pneumatic tire mounted on a vehicle. The sensors are load cells mounted flush with the roadbed, i.e., there is no bar and thus no deformation of the tire other than that naturally occurring due to the load carried by the tire. Tire pressure distribution on the road surface is used, not total weight.
U.S. Pat. No. 2,126,327 to Hendel et al. does not use car weight in its analysis and does not use a bar. It makes some measurement of tire "force" distributed between a bladder and the surrounding road surface, but the bladder is not elevated above the roadbed. Rather, it is recessed, so tire deformation is not used in the process and total tire weight is not used.
U.S. Pat. No. 2,663,009 to Finan discloses a system for making an on-vehicle measurement of tire softness, not a road surface measurement. Something like a bar is used, but it does not measure total weight. This system can be calibrated for the specific tire on the specific vehicle whereas Applicant's invention will accommodate a wide variety of tires and vehicles.
U.S. Pat. No. 2,313,156 to Kratt, Jr., measures the force profile across the tire, the same approach used in the Rosensweig patents. Tire deformation is not used and total tire weight is not used.
U.S. Pat. No. 3,715,720 to Jehle involves depressing a probe (point measurement as opposed to across the whole tire) which is maintained at a specified force. Total weight is not used.
In U.S. Pat. No. 3,973,436 to Linderman, force distribution across the tire is measured, similar to U.S. Pat. No. 2,313,156. Neither a bar nor total weight is used.
U.S. Pat. No. 5,289,718 to Mousseau discloses a method for measuring the force exerted by the tire in going over a step. It does not use a bar or total weight, and is not intended for underinflation measurement but for measurement of tire force on rough surfaces. No means is described for extracting inflation-related information.
2. Description of the Invention
It is an object of the invention to provide an improved tire checker.
To this end, the apparatus for determining the inflation status of a vehicle tire according to the invention comprises a scale plate installed in a road surface, said scale plate being supported by at least one load cell; recording means connected to said at least one load cell for recording the weight Y on said scale plate with respect to time; a deformation bar located in said road surface and supported by at least one load cell, said deformation bar being raised above said road surface and adapted to deform said tire when said tire rolls over said deformation bar; and a recording means connected to said at least one load cell for recording the weight X on said deformation bar with respect to time.
It is also an object of the invention to provide a method of determining the inflation status of a vehicle tire.
To this end, such a method according to the invention comprises recording a first signal representing the weight on said tire with respect to time when the tire is rolling on a flat surface; recording a second signal representing the weight on said tire with respect to time when the tire is rolling over a raised object; determining the maximum Y of the first signal and the maximum X of the second signal; calculating a ratio R by dividing the maximum X of the second signal by the maximum Y of the first signal; and comparing the calculated ratio R (=X/Y) with a predetermined value for the ratio R pertaining to the maximum Y of the first signal and giving an underinflation signal if the calculated ratio is below the predetermined value.